Peripheral arterial disease (PAD), caused by atherosclerosis that impairs blood flow to the lower extremities, is a major health problem. Currently there are no medical therapies for PAD that have the ability to increase perfusion and correct the impaired blood flow. Therapeutic angiogenesis is a strategy to treat patients that have inadequate tissue perfusion. However, therapeutic angiogenesis trials in humans have almost uniformly failed and these failures may be attributable to the use of simple regimens and approaches that were designed without an adequate appreciation of the complexities that regulate the numerous competing ligands, receptors, and modulators within a given target tissue. To understand these phenomena at the fundamental level and to develop novel therapeutic approaches, quantitative computational systems biology approaches synergistically combined with experimental measurements are not only desirable, but absolutely necessary. The broad goal of the project is to gain a quantitative knowledge and understanding of angiogenesis in PAD, using a highly synergistic combination of predictive multiscale computational modeling and in vivo experiments; and further, using this knowledge, to design improved and novel human therapeutics. The proposed experimental studies are driven by the current predictions of the computational models. The proposed multiscale models will connect the levels from the molecular, to cellular, to microcirculatory, to tissue, and finally to whole body. The experimental measurements will similarly be conducted at multiple scales, using vascular endothelial growth factor (VEGF) and the VEGF receptors, viable targets for the modulation of therapeutic angiogenesis, from the molecular to the tissue and systemic measurements. The use of mouse models of PAD that reflect the strong association of human disease with diabetes and hypercholesterolemia which occur in the majority of patients with PAD in human, as well as human samples, reflect that the proposed work has an important translational component. The first three specific aims will examine mouse models. The first aim will characterize a model with excellent perfusion recovery. The second aim will examine models of impaired angiogenesis and the third will examine predictions of efficacy of gene transfer. The last aim will examine human tissues that parallel the situations created within the mouse models.